A refinement of the crystal structure of quinolinic acid at 100 K with neutron diffraction data

Abstract

The crystal structure of quinolinic acid (pyridine-2,3-dicarboxylic acid: C7H3N04 ) has been refined, based upon neutron diffraction data measured at 100 K. Crystal data: space group P2l/cm, a — 7-415 (5), b = 12-396 (9), c = 7-826 (6) A, P = 117-05 (4)°, Z = 4. The final unweighted R value based on F2 is 0-048 for all 1643 unique reflections, and bond distances have been determined with precision better than 0-003 A. The major temperature dependence in the cell constants is observed for the b axis, which is perpendicular to the molecular planes. Rigid-body analyses of the thermal parameters determined here at 100 K and those found in a prior study at 297 K indicate that the translational motion changes with temperature more along the b axis than in other directions. Significant differences between the structure at 100 and 297 K are observed in the intramolecular O • • • H • • • O hydrogen bond, where the H atom shifts towards the midpoint of the bond when the crystal is cooled. This temperature effect is discussed in the light of results of the rigid-body thermalmotion analyses.